Referring to FIGS. 8 and 9, a conventional solenoid valve for irrigation systems comprises a connecting tube (50), a valve piece (60) and a solenoid valve (70). The connecting tube (50) has a water inlet tube (52) and a water outlet tube (53), and a valve tube (51) is formed therebetween and configured to separate the water inlet tube (52) and the water outlet tube (53). The valve piece (60) installed in the valve tube (51) is configured to control water flow passing from the water inlet tube (52) to the water outlet tube. The solenoid valve (70) has a magnetic member (71) installed therein, and a metal plate (72) is installed at an end of the solenoid valve (70) which is located away from the valve piece (60). Moreover, the valve piece (60) is connected to a metal ring (61). When the solenoid valve (70) is energized to generate magnetic field which pushes the magnetic member (71) to bear against the valve piece (60), the valve piece (60) is configured to tightly press the valve tube (51) so as to stop water flowing from the water inlet tube (52) to the water outlet tube (53). Meanwhile, the magnetic member (71) is adapted to stick to the metal ring (61) of the valve piece (60). On the other hand, when reverse current is provided to pass through the solenoid valve (70), the magnetic member (71) is configured to detach from the valve piece (60) and to move toward and stick to the metal plate (72) of the solenoid valve (70) so as to enable water to flow from the water inlet tube (52) to the water outlet tube (53).
However, the conventional solenoid valve for irrigation systems is disadvantageous because: (i) the metal ring (61) and the metal plate (72) are respectively arranged adjacent to two ends of the magnetic member (71), and in order to prevent the valve piece (60) from simultaneously attracting both the metal ring (61) and the metal plate (72), the shifting distances between the metal ring (61) and the magnetic member (71) and between the metal plate (72) and the magnetic member (71) need to be increased, which prolongs the on/off switch time of the solenoid valve (70); (ii) electricity is needed not only in detaching the magnetic member (71) from the metal ring (61) or the magnetic member (71) but also in pushing the valve piece (60) between the metal ring (61) and the metal plate (72), which consumes large amount of power; and (iii) the metal ring (61) of the valve piece (60) which is soaked in water is prone to get rusty thereby reducing the quality of spraying water and leading to the damage of the valve piece (60). Therefore, there remains a need for a new and improved design for a solenoid valve for irrigation systems to overcome the problems presented above.